GB2087526A - Improvements in and relating to regenerative heat exchanger apparatus - Google Patents

Abstract

A refractory wall 27 for a combustion chamber 11 comprising a plurality of wall portions which include refractory blocks 28 having generally horizontal, front-to-back passageways interspersed with a plurality of portions which include unperforated refractory blocks 30. Outwardly of each perforated block portion a regenerative heat-exchange section 13 is located with the perforated block portion serving to retain heat- exchange elements in that section and to resist their considerable lateral thrust. At the same time the perforated portions are integrated with the non-perforated portions to form a continuous circular wall of superior strength and resistance to elevated temperatures as well as to chemical attack. The apparatus is used for purifying effluents from industrial processes. <IMAGE>

Description

SPECIFICATION Improvements in and relating to heat exchange apparatus Field of Invention This invention relates to heat exchange apparatus and, in particular to a refraction structure comprising a perforated inner retaining wall made of refractory block for exchange apparatus.

Prior Art and Background to the Invention Recently, with the advent of ever-higher energy cost figures, there has been a correspondingly increased demand for apparatus which can conserve heat therey reducing fuel costs. One such apparatus which is usable especially in thermal regenerative apparatus for pollution control, for example, is shown in U.S. Patent 3,895,918 issued to James H. Mueller on July 22, 1 975. As shown in that patent, there is a central high temperature combustion or incineration chamber surrounded at equi-angularly spaced intervals by a number of contiguous heatexchange sections. These sections communicate with the combustion chamber and with an external supply of pollutants such as noxious effluents from industrial processes.The effluents are applied by employing automatic dampers to predetermined ones of the heat-exchange sections during any given cycle of operation. In each section, there is a heat-exchange bed made of a number of ceramic heat-exchange elements which are retained outwardly by a perforated steel wall and inwardly (closest to the combustion chamber) by another perforated or louvered metallic wall.

Since a great quantity of heat exchange elements are poured into the space between these two retaining walls, there is a great amount of lateral thrust exerted by their combined weight.

When the effluents are passed through a predetermined one or ones of the heat-exchange sections during a processing cycle, their temperature is increased by the residual heat in the ceramic elements of that section gained in a previous cycle when gas purified in the combustion chamber was drawn through that section to exhaust. After being preheated in that section, the incoming effluents enter the combustion chamber where their harmful components are oxidized. The purified effluent is then drawn out of the combustion chamber through others of the heat-exchange sections into the exhaust circuit for dispersion to the ambient atmosphere.

In such heat regenerative structures, the considerable lateral thrust of the ceramic heat exchange elements often required the use of steel tie rods extending horizontally between the front retaining wall ("hot face") and the rear retaining wall ("cold face"). These tie rods, as well, prevented bowing or deflection of the hot face due to heat. At the ends of these rods special Belleville washers and nuts were used to adjust the tension of the rods. Special horizontal pins were also lodged in the side edges of the front retaining wall for added structural strength. At incineration temperatures of up to about 1 20OC1 6000F, the hot face was often made of very expensive material such as high nickel-chromium content steel having low creep.For operation of the combustion chamber at even more elevated temperatures such as in the 16000--18000F region, considerably more of this expensive steel would be required.

Moreover, the front retaining wall in conventional apparatus was often subjected to attack by the corrosive or other chemically destructive effects of some constituents of the effluents resulting in shortened life of such metallic walls. The front retaining walls of metal also had no substantial heat-exchange qualitites.

Checker-board refractory walls have been used conventionally to provide heat-exchange properties, but, in general, they are so constructed as to be unable to withstand a considerable load.

While U.S. Patent 2,125,193 does show refractory blocks with grooves on one side which are disposed with the grooves of adjacent blocks to form an axial opening for permitting oxygen flow through the openings, there is no teaching of a horizontal arch-like wall consisting of a number of refractory blocks having axial passageways extending through them integrated into a circular combustion chamber wall. Such curved wall serves as an additional heat exchange assembly that can more economically withstand higher combustion temperatures and chemical attack and resist lateral thrust pressures.

It is therefore among the objects of the present invention to provide a refractory wall which: (1) Is more temperature resistant than conventional walls used in heat-exchange apparatus.

(2) Is less expensive to erect and to maintain than comparable known walls.

(3) Is more resistant to chemical attack than conventional walls.

(4) Is productive of yreater heat-exchange effects than conventional metallic retaining walls.

(5) Is capable of imparting greater strength to the overall furnace wall into which it is integrated than conventional metal-concrete constructions.

Summary of the Invention According to the present invention a combustion chamber wall has at least one portion comprising a plurality of refractory blocks perforated by a plurality of generally horizontal passageways. The blocks are laid in contiguous fashion in a generally horizontal arch-shaped array in front of a plurality of heat-exchange elements which it helps to retain. In one embodiment, the blocks are interspersed with unperforated bricks to form an integrated circular refractory assembly.

Brief Description of the Drawings Fig. 1 is a plan view, partly broken away, of thermal regenerative apparatus in which the present invention may be employed; Fig. 2 is a perspective view looking outwardly from the combustion chamber showing the novel perforated-brick retaining wall in accordance with the present invention; Fig. 3 is a fragmentary, partly sectional plan view of the retaining wall shown in Fig. 2; and Fig. 4 is a fragmentary side elevation view taken along view line 4-4 in Fig. 3.

Detailed Description of the Drawings Fig. 1 shows a thermal regenerative apparatus generally at numeral 10 in accordance with the teachings of the aforesaid Mueiler patent. It includes a central, domed combustion chamber 11 with burners 21 projecting therein. Around chamber 11 are disposed, at equal spaces, a plurality of sections 12 each of which includes a perforated outer retaining wall 23 and, inwardly thereof, a heat-exchange bed 13 in which a large number of refractory heat-exchange elements 24 are disposed. Industrial effluents are applied via inlet duct 1 7 to a generally toroidal inlet ring 1 6 that is coupled via feeder duct 9 (Fig. 2) to the spaces 20 outwardly of outer retaining wall 23.

An inlet valve 14 is disposed in each feeder duct 9 to enable cycle changes. Another duct 26 having a valve 26a passes into space 20 through top wall 25 covering each heat exchange section for introducing "purging" gas as mentioned in the cited Mueller patent, if desired. Also attached to each section 12 is an outlet duct 8 having an outlet valve 1 9 disposed therein. Ducts 8 communicate with spaces 20 and with outlet toroidal ring 1 5 to which exhaust duct 18 is also coupled. Duct 1 8 may be connected to an exhaust blower and a stack.

As shown in Figs. 2 and 3, the refractory elements 24 are retained outwardly by perforated metal plate or wall 23 and toward the center by a curved combustion chamber wall indicated generally at numeral 27 (Fig. 2). Wall 27 comprises a plurality of portions which include perforated refractory bricks 28 laid in curved rows as shown in Figs. 2 and 3. These curved wall portions 27a are interspersed with other curved, circular wall portions, 27b consisting of arrays of unperforated bricks 30 to form a continuous curved (cylindrical) lining for the combustion chamber 11.

Behind the unperforated bricks 30,31 and 32, is an outer wall 34 consisting of, for example, "Monoblock" or other commercially available high temperature insulating material which may be either of the low density or high density type.

Surrounding and supporting the refractory bricks 30, 31 and 32 is a metal shell 35 which also surrounds each heat exchange section 12.

As seen best in Figs. 2, 3 and 4, each of the refractory bricks 28 has a number of axial passageways 28b to enable effluents that have been unpurified to enter or leave the combustion chamber 11 for processing or for exhaust, respectively. The particular refractory blocks 28 shown have perforations 28b comprising one third of the vertical cross-section of the block. This ratio has been found to enable the thermal efficiency of the overall apparatus in particular installations to be maintained by not introducing an unnecessarily high pressure drop while allowing adequate flow for full purification in the combustion chamber. Of course, each installation may impose its own requirements on the number or size of perforations for the block.

Each block 28 also has, in the embodiment shown, a vertical ridge 28a positioned on one side which is designed to mate with the corresponding groove 28c formed on the opposite side of the brick adjacent to it. Each block in the embodiment shown in Figs. 2, 3 and 4 has a horizontal crosssection as shown in Fig. 3 which facilitates the erection of a horizontal, arch-shaped, retaining wall portion 27a inwardly of each heat-exchange bed 13 and thus the entire wall structure 27 has a high hoop strength. The blocks 28 extend generally in front of the opening formed by the non-parallel walls of each heat-exchange section 12. Unperforated bricks 31 and 32 as shown in Fig. 2 form the transition between the blocks 28 and bricks 30.

The perforated refractory block retaining wall shown in the drawings has been found to effect considerable cost savings compared to the flat, rigid metallic inner retaining wall of the prior art.

Its erection is merely a masonry project not requiring special steels, special washers, special tie rods, special side-pins and other equipment and assembly costs. Its operation also achieves cost savings as it can withstand higher combustion chamber temperatures and their adverse effects without resort to the very expensive special steels which would otherwise be required. Those steel walls are, in any event, more vulnerable to chemical attack than refractory materials and cannot enhance the heat-exchange properties of the apparatus as refractory materials can.

Claims (9)

1. In heat-exchange apparatus. the combination comprising: (a) a central high temperature combustion zone, (b) a wall having a generally closed curve configuration surrounding said zone and made principally of a plurality of refractory blocks, said wall having a first plurality of portions in which said blocks are perforated interspersed with a second plurality of portions which are unperforated, (c) a plurality of heat exchange sections disposed outwardly of said wall but in contiguity therewith, each section being located at one of said first plurality of portions in which said blocks are perforated, each section including a wall member which, with said perforated portion, retain a plurality of heat exchange elements, said wall members having a part permitting gas flow through said elements to or from said zone, and (d) means coupled to said sections for bringing purified or unpurified effluents to or from said sections.

2. The combination according to claim 1 wherein said wall is substantially circular and the blocks of said first plurality are laid next to one another in a number of adjacent horizontal rows.

3. The combination according to claim 1 wherein the perforations of the blocks of said first plurality are a plurality of passageways extending from the front to the back of each such block.

4. The combination according to claim 3 wherein said passageways of each block constitute about 3040% of the volume thereof.

5. The combination according to claim 1 wherein each block of said first plurality has a ridge on one side and a groove on the other whereby adjacent ones of said blocks can mate with one another.

6. The combination according to claim 1 wherein said circular wall has substantially uniform thickness but the thickness of the wall at said first plurality of portions is made up solely by the front-to-back dimensions of a single brick whereas the thickness of the wall at said second plurality of portions is made up of at least two horizontally displaced but abutting vertical sets of refractory bricks.

7. The combination according to claim 1 wherein the outer side of said wall portions and said heat exchange sections are sheathed in metal.

8. In heat exchange apparatus having a generally centrally disposed high temperature combustion zone surrounded by a wall having a plurality of spaced portions made of refractory material, the combination comprising: (a) a plurality of heat-exchange sections disposed outwardly of but contiguous with said wall at the spaces thereof between said portions of refractory material, each section including an inner retaining wall and a perforated outer retaining wall for holding a plurality of discrete heat exchange elements piled on one another, said inner retaining wall comprising a plurality of perforated refractory blocks disposed in a generally closed curve configuration whose concave portion faces said zone, and (b) means coupled to said sections for bringing purified or unpurified effluents to or from said sections.

9. Heat exchange apparatus constructed, arranged and adapted to operate substantially as herein described with reference to and as illustrated in the accompanying drawings.